A processing step of separating a conglomerate materials into various components has proved highly valuable in modern industrial processes. Many different separation techniques have been utilized in the past with these techniques relying on differing characteristics of the components, such as size, weight, specific gravity and the like, which constitute the material. It has long been recognized in certain industrial processes that the separation of a particulate material into magnetic and non-magnetic components has particular utility. Among various magnetic separation apparatus is that known as the high-intensity magnetic roll separator, and this separator has particular applications in the dry separations of particulate materials.
Typically, magnetic roll separators are configured to have a cylindrical magnetic roller located at a downstream end, a cylindrical idler roller located at an upstream end and a relatively thin conveyor belt encircling the magnetic roller and the idler roller. Material to be separated is deposited in an upper conveying portion of the belt at an upstream end so that it is advanced towards the downstream and is discharged as the conveyor belt moves around the magnetic roller. Magnetic components are attracted to the magnetic roller and thus have a different discharge trajectory than non-magnetic components as the various particles leave the conveyor belt at the discharge region associated with the magnetic roller. The difference in discharge trajectories results from the fact that non-magnetic components are affected only by a gravitational force and the "centrifugal force" while magnetic components are subjected not only to "centrifugal" and gravitational force but also to the magnetic force attracting the particulate material to the magnetic roller. This magnetic attraction causes the magnetic components to "cling" to the conveyor belt adjacent the magnetic roller for a slightly longer period of time than the non-magnetic components as the conveyor belt advances around the magnetic roller. The discharge component streams may accordingly be collected in a collection bin provided with suitably positioned deflectors to separate the different streams of particles. This procedure may be repeated over multiple stages to obtain an increasingly refined product.
One problem that has confronted magnetic roll separators, however, is conveyor belt drift as the conveyor belt tracks around the pair of rollers. This belt tracking difficulty encountered with magnetic roll separators stems from the fact that the length of the rollers are long relative to the distance of separation between the magnetic roller and the idler roller (the "roller distance"). This fact, coupled with the need for relatively thin belts necessary to achieve strong effective magnetic forces, militates against incorporation of conventional belt tracking systems with magnetic roll separators. For example, the use of shaped rollers, either crowned or convex, is inappropriate since the roller distance must be substantially increased so that it is much greater than desired from an optimum configuration for materials processing. This limits the separator capacity due to the maximum load limit on the belt to avoid excessive sagging. Further, the thin conveyor belts used for magnetic roller separation are constructed of materials such as Kevlar.RTM. (a trademark of the DuPont Corporation) fabric, in order to have substantial strength while keeping the belt thin. These belt fabrics have relatively small elasticity which limits the advantages of configured rollers. Accordingly, magnetic roll separators that employ configured rollers either operate with thick belts or operate with less than optimum processing capacity.
Another conventional belt tracking technique utilizes mechanical guides to confine the conveyor belt in a desired tracking path. A major disadvantage, here, is the susceptibility of the conveyor belts to failure due to stress caused by the mechanical guides, such as pins, studs, guiderails and the like. In order to reduce belt failure, the thickness of the belts are increased which again results in reduced performance of the separation since the magnetic force decreases proportionally with an increase in the thickness of the belt.
Accordingly, there remains a need for improved belt tracking structure which simultaneously allows the use of a relatively thin belt having a short roller distance and which system minimizes the stress placed on the belt during operation.